Second master was a rating introduced into the Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 in 1753 that indicated a deputy master

Master (naval)

The master, or sailing master, was a historic term for a naval officer trained in and responsible for the navigation of a sailing vessel...

 on third-rate

Third-rate

In the British Royal Navy, a third rate was a ship of the line which from the 1720s mounted between 64 and 80 guns, typically built with two gun decks . Years of experience proved that the third rate ships embodied the best compromise between sailing ability , firepower, and cost...

 ships of the line

Ship of the line

A ship of the line was a type of naval warship constructed from the 17th through the mid-19th century to take part in the naval tactic known as the line of battle, in which two columns of opposing warships would manoeuvre to bring the greatest weight of broadside guns to bear...

 or larger.

Second masters were paid significantly more than master's mate

Master's mate

Master's mate is an obsolete rating which was used by the Royal Navy, United States Navy and merchant services in both countries for a senior petty officer who assisted the master...

s, £5 5s per month. A second master was generally a master's mate who had passed his examination for master and was deemed worthy of being master of a vessel. Second masters were given the first opportunity for master vacancies as they occurred.

Master's mates also acted as second master of vessels too small to be allocated a warranted master.